1. Field of the Invention
The present invention relates to a high-pressure liquid supply pump, and more particularly to a high-pressure fuel supply pump capable of avoiding an abnormally high fuel pressure.
2. Description of the Related Art
In a high-pressure fuel supply pump disclosed in JP-2003-343395-A, a relief valve (check valve) is incorporated as a safety valve with its outlet connected to a low-pressure piping. More specifically, an intake path and a delivery path of the fuel supply pump are positioned close to each other and interconnected with a communication path in which the relief valve is installed. This makes it possible to remove a relief piping from an engine while the fuel pump is of a small size.
The valve structure disclosed in JP-58-004778-U avoids chattering of a relief valve that is used as a safety valve. When the delivery pressure of a lubrication pump unduly rises, this relief valve is relieved to avoid damage, for instance, to a supply pipe connected to the lubrication pump and component parts of the lubrication pump. More specifically, a first operating valve and a second operating valve are used. These valves have a first pressure reception surface and a second pressure reception surface, which differ in pressure reception area. When pump pressure acting on the first pressure reception surface opens the first operating valve, a force considerably greater than the force applied to a valve seat acts on the second pressure reception surface and moves the valve to its terminal position. Therefore, the relief status can be indicated steadily and definitely by using an indicator that operates in coordination with a valve disc.